The present invention relates to a toner for developing an electrostatic latent image and an image forming method.
It has been known that technology for producing a toner for developing an electrostatic latent image, for example, a production of toner by a suspension polymerization has been practically performed.
However, the toner particle obtained by the suspension polymerization has a shortcoming that the toner is inferior in the fixing property since the toner has a spherical shape.
Besides, it has been known a method for obtaining an irregular-shaped, not spherical, toner particle in which a resin particle prepared by an emulsion polymerization process and a colorant particle are associated by coagulation or fusion-adhesion, example of the method is described in Japanese Patent Publication Open to Public Inspection, hereinafter referred to JP O.P.I., No. 5-265252.
Moreover, in a fixing method by a contact heating using a heating member such as a heating roller, the toner is required to have a releasing ability from the heating member, hereinafter referred to an anti-offset ability, and an anti-winding property of the image support to the heating member, hereinafter referred to an anti-winding ability.
It is necessary to be used a resin having a high molecular weight to obtain a toner excellent in the anti-offset ability and the anti-winding ability.
On the other hand, it is necessary to be used a high molecular weight as the resin constituting the toner particle to obtain a high adhesiveness of the toner to the image support or image receiving paper.
Therefore, it is preferable, for obtaining a toner excellent in the anti-offset ability and the anti-winding ability while maintaining the adhesiveness to the image support, that the toner particle contains a low molecular weight resin having a peak at a low molecular weight region of the molecular weight distribution and a high molecular weight resin having a peak at a high molecular weight region of the molecular weight distribution, namely the molecular weight distribution has two peaks.
(1) When the toner particle comprising a low molecular weight resin and a high molecular weight resin is produced by associating a resin particle with a colorant particle, a resin particle comprising the low molecular weight resin, a resin particle comprising the high molecular weight resin and the colorant particle have to be associated, coagulated and fusion adhered, in an aqueous medium.
However, the individual toner particles of the toner obtained by such the method tend to be different from each other in the molecular weight of the resin component or the composition of the resins, for example, composition ratio of the low molecular weight resin to the high molecular weight resin. Therefore, the improvement of the anti-offset ability and the anti-winding ability cannot be sufficiently obtained by the introduction of the high molecular weight resin.
(2) JP O.P.I. No. 9-265210 describes a toner production process comprising the step for preparing a combined particle containing a resin component having two peaks in the molecular weight distribution and a colorant (a colorant-containing composite resin particle) formed by twice repeating an emulsion polymerization of an ethylenic unsaturated monomer, and the step for associating (coagulating and fusion-adhering) thus obtained colorant-containing composite resin particles.
The difference of the molecular weight or the composition of the resin between the individual resin particles can be reduced in some degree by such the method since the composite resin particles (resin particles having two peaks in the molecular weight distribution) are associated.
However, the following problems are raised in the toner produced by the method described in the foregoing publication since the polymerization of the monomer is performed in the presence of the colorant.
(a) The composite resin particle (the colorant-containing composite resin particle) having the expected molecular weight cannot be obtained because the polymerization reaction of the monomer is inhibited by the presence of the colorant in the polymerization system. Such the toner tends to cause the stain in the fixing device or on the image since which is occurred by the resin component having a molecular weight of not reached to the expected value (a resin component having a low fusion viscosity).
(b) The monomer and an oligomer thereof are remained in the toner as a result of inhibition of polymerization by the colorant, and bad smell is given out some times in the course of image formation using the toner.
(c) The surface property of individual particles is varied from each other as a result of the inhibition of the polymerization reaction so that uniform polymerization is not performed. Accordingly, the distribution of the charged amount is made broad and the sharpness of the image formed by the toner is degraded some times.
According to the foregoing situation, the inventors have proposed a toner obtained by salt-out/fusion-adherence of the composite resin particle with the colorant particle and a producing method thereof, cf. JP O.P.I. No. 11-95889.
The toner described in this publication is excellent in the uniformity of the composition, the molecular weight and the surface property of each toner particles, and the anti-offset ability and the anti-winding ability can be improved while maintaining the adhesiveness (fixing ability) and a visual image having a high sharpness can be formed for a long period of time by the use of such the toner.
Introduction of a releasing agent into the toner particle is considered to further improve the anti-offset ability of the toner. Moreover, introduction of crystalline polyester as a fixing ability improving agent into the toner particle is considered to further improve the anti-offset ability of the toner.
To introduce the releasing agent and/or the crystalline polyester, a method in which an emulsion comprising a particle of the releasing agent and/or the crystalline polyester dispersed in water is added at the salting-out/fusion-adhering process for salting-out/fusion-adhering together with the composite resin particle and the colorant particle.
However, it has been experimentally confirmed by the inventors that the toner particle produced by the salt-out/fusion-adherence of the resin particles, the colorant particles and the particles of the releasing agent and/or the crystalline polyester is insufficient in the crush resistivity.
It is considered as the reason of the above fact that a continuous phase of the releasing agent and/or the crystalline polyester (a relatively large domain which functions as a stating point of the crush) exists at the interface of the resin particle.
As a result of that, a risk of occurrence of filming, fogging or toner spending is raised when the toner produced by the association of the releasing agent particle and/or the crystalline polyester particle is used to image formation for a long period of time
Recently, development of a toner is strongly demanded which is able to be fixed at a temperature lower than that of an usual toner according to requirements of miniaturization and reduction of electric consumption of a copy machine. Therefore, it is preferred that the toner has a wide range (a fixing performable temperature range) from the lowest temperature at which the fixing can be performed (the lowest fixing temperature) to the highest temperature at which the offset phenomenon is not occurred.
However, it has been experimentally found by the inventors that the toner prepared by the salt-out/fusion-adherence of the resin particle, the colorant particle and the releasing agent particle and/or the crystalline polyester particle has not the sufficiently wide fixing performable range.
The first object of the invention is to provide an associated type toner and a producing method thereof, which is constituted by a resin having a designated molecular weight distribution and the variation of the composition, molecular weight and the surface property between the individual particles is small.
The second object of the invention is to provide an associated type toner and a producing method thereof, which has a high anti-offset ability and a high anti-winding ability while maintaining a sufficient adhesiveness to the image support.
The third object of the invention is to provide an associated type toner and a producing method thereof, which does not give off a bad smell in the process of image formation and the fixation by heat.
The fourth object of the invention is to provide an associated type toner and a producing method thereof, which is excellent in the charging property and capable of forming an image having a high sharpness.
The fifth object of the invention is to provide an associated type toner and a producing method thereof, which is excellent in the anti-crush property and does not form a fine powder causing filming, fogging and toner spending.
The sixth object of the invention is to provide an associated type toner and a producing method thereof, which has a wide fixing performable temperature range.
The seventh object of the invention is to provide an image forming method using the foregoing excellent associated type toner.
A toner production method a comprising (I) the step for forming a composite resin particle by a multi-step polymerization process, which contains a releasing agent or a crystalline polyester compound in a portion other than the outermost layer, and (II) the step for salting-out/fusion-adhering the composite resin particle with a colorant particle.
A toner production method comprising the step (I) for forming a composite resin particle by a two-step polymerization process, which has a central portion (core) comprising a high molecular weight resin having a peak or shoulder molecular weight within the range of from 100,000 to 1,000,000 and an outer layer (shell) comprising a low molecular weight resin having a peak or shoulder molecular weight within the range of from 1,000 to 50,000, and the central portion (core) contains a releasing agent or a crystalline polyester compound, and (II) the step for salting-out/fusion-adhering the composite resin particle with a colorant particle.
A toner production method comprising (I) the step for forming by a three-step polymerization process a composite resin particle which has a central portion (core) comprising a high molecular weight resin having a peak or shoulder molecular weight within the range of from 100,000 to 1,000,000, an interlayer comprising a resin having a peak or shoulder molecular weight within the range of from 25,000 to 150,000 and an outer layer (shell) comprising a low molecular weight resin having a peak or shoulder molecular weight within the range of from 1,000 to 50,000, and the interlayer contains a releasing agent or a crystalline polyester compound, and (II) the step for salting-out/fusion-adhering the composite resin particle with a colorant particle.
A toner production method comprising the step for forming a system by adding a resin particle to be a central portion of a combined particle into an aqueous solution of a surfactant and dispersing a monomer composition containing a releasing agent or a crystalline polyester compound in the solution, and the system is subjected to a polymerization treatment.
In an image formation method described above, the method comprises the step for fixing the image by a directly heating process, in which the foregoing toner is used for image formation.